Wall surface panel capable of generating minus ions utilizing natural volcanic ash soil

ABSTRACT

A wall is formed by adding a predetermined amount of binding agent and water to volcanic ash sediment, which is comprised of mineral silicate including at least silicic acid and aluminum oxide, kneading them, and applying to an arbitrary plane. Through a natural reaction of positive ions included within mineral silicate and moisture included within the atmospheric air, thereby exchanging ions, minus ions are generated on an application plane. The amount of minus ions generated is, in a unit volume, between three and six times as many as that of the minus ions generally included in the atmospheric air. The combination of this application plane and humidity control apparatus is used as a minus ion generation system through adjustment of amount of moisture included within the atmospheric air so as to control the ion exchanging rate. In the case where said volcanic ash sediment includes titanium oxide, it reacts with hydrogen or oxygen generating active oxygen species or oxygen free radical. Using this function of generating the active oxygen species, the application plane is utilized as an air filter.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a system and method foreffectively generating minus ions by utilizing negative ion exchangefunctionality included in material for walls, based on the discoverythat wall surfaces made of natural volcanic ejecta (volcanic ashsediment) as a main component have high minus ion generationfunctionality.

[0003] 2. Related Background Art

[0004] In recent years, study in the utilization of “shirasu”, avolcanic ejecta and found in abundant deposits, has been carried out inthe field of construction. Shirasu is a generic name given to whitelumps of volcanic ejecta and the secondary sedimentation originatingtherefrom, which are widely distributed about the Southern Kyushu areaof Japan. Conventionally, almost all examples of using shirasu have beenas building material that has undergone secondary processing; however,the inventor implements non-processed shirasu as a finishing coatmaterial to be used in construction (U.S. Pat. No. 6,171,655 andJapanese Patent Application No. 2000-391856), and is experiencingcommercial success.

[0005] Crystallization differentiation occurs due to the cooling ofhigh-temperature magma, thereby clustering and crystallizing the maincomponents of magma, for example, SiO₂, Al₂O₃, Fe₂O₃, FeO, MgO, CaO,Na₂O, K₂O together into minerals. Soon thereafter these are violentlyejected, forming this shirasu. Shirasu comprises approximately 30%crystallized minerals and approximately 70% non-crystalline volcanicglass.

[0006] Non-crystalline volcanic glass takes on a porous pumice-likeconstitution due to the vigorous emission of the volatile components ofmagma, and comprises 65 to 73% SiO₂, 12 to 16% Al₂O₃, 2 to 4% CaO, 3 to4% Na₂O, 2 to 4% K₂O, and 1 to 3% iron. The crystallized mineralscomprise mostly plagioclase, but also include some hypersthene, quartz,augite, magnetite and the like.

[0007] Examples given for shirasu processing include the utilization of“shirasu balloons”, which are obtained through rapid heating. Whenshirasu is heated, softening of glass contained in the shirasu andevaporation of water contained in the shirasu occur at the same time tocause foaming, and forming the hollow spherical bodies of what isreferred to as “shirasu balloons” (developed in 1970 by Kyushu KogyoGijutsu Shiken Kenkyusho). Shirasu balloons are naturally producedthrough high-temperature heating by magma, and are included withinshirasu. The approximate size of shirasu balloons naturally included inshirasu range from 30 to 600 μm, and characteristics include being nonflammable, a low bulk density, a high melting point, low thermalconductivity, low dielectric constant, non-toxic, and do not emit toxicgas. In recent years, shirasu balloons having sizes ranging from 600 to3000 μm have been artificially produced. Light-weight industrialcoatings capable of thick application have been produced by secondaryprocessing of such shirasu balloons. In addition, usage in constructionmaterials such as for ceiling materials that are light and do notrequire much strength has also come to enjoy full-scale use; moreover,progress in the development of polymer composite materials usingpulverized shirasu is continuing.

[0008] In comparison with technology where shirasu undergoes secondaryprocessing, direct commercialization of non-processed shirasu has notexisted for very long. This is due to the fact that shirasu hasextremely high flow properties in water. Evidence of the high flowproperties in water can be seen in, for example, conditions where groundlevel shirasu is eaten away and countless eroded valleys have appeared.

[0009] If amalgamated substance of shirasu and water is applied as it isas material for a wall, cracks will appear in the surface when it dries.Furthermore, in addition to cracks in the surface due to drying, a waterflow phenomenon also occurs, where water in the surface of the walldescends and flows down on the surface of the wall.

[0010] The inventors have overcome problems such as cracks and waterflow by adding a predetermined percentage of a predetermined materialthat includes a clay component having high water-retentiveness and haveachieved commercialization of a wall material that effectively uses thenatural volcanic ash material shirasu, as disclosed in theabove-mentioned U.S. patent. Not only is this wall material currentlyenjoying commercial success, but is also gaining favorable evaluationfrom, for example, the Kyushu Kogyo Gijutsu Shikenjo, the KagoshimaPrefectural Institute of Industrial Technology (in particular, theMaterials Division), and the Miyazaki Prefecture Industrial TechnologyCenter. The development and commercialization of shirasu wall materialshas had an extremely high effect on market activity such that the priceof shirasu volcanic ash, which used to be traded in the neighborhood ofJPY3000 per 10 tons, has become approximately JPY10,000 per 10 kg.

SUMMARY OF THE INVENTION

[0011] In recent years, the inventors have found a novel effects of wallmaterials containing natural shirasu as a main component. The firsteffect thereof is a minus ion generating effect based on weak ionexchange functionality with shirasu, which is a natural volcanic ejecta.The second effect is a sterilizing and deodorizing effect by activeoxygen species (i.e., oxygen free radicals) generated through reactionwith moisture and/or oxygen included in the air, which has also beenconfirmed. These effects may be efficiently brought out when the naturalshirasu wall material is applied onto a plane such as a wall and a panelsecuring a sufficient surface area.

[0012] More specifically, the minus ion generating effect has beenmeasured and confirmed by the inventors as generating a level of minusions that is one digit higher than that of minus ions existing in theair at room temperature at normal humidity. Such minus ion generatingeffect is not lost even at high humidity or during the rainy season, forexample. Rather, when a water mist is sprayed onto a wall surface, theminus ion effect is strongly brought out; this effect should bedistinguished from the Lennard effect (waterfall effect), as isdescribed later.

[0013] The Lennard effect is the effect where the surface area of waterchanges, or for example, water drops splashing at the base a waterfallsplit, positively charging the split water drops themselves andnegatively charging the ambient air. In contrast, since the generationof minus ions from the wall surface applied with a wall material havingnatural shirasu as a main component is a continuous generation of minusions based on a weak ion exchange functionality with the inside of wallmaterials, it is different from an instantaneous generation of minusions due to splitting of water drops such as generation by the Lennardeffect.

[0014] The weak ion exchange functionality of shirasu is considered toemanate from the existence of mineral silicate configuring the shirasu.The mineral silicate having shirasu as a main component has a structurewhere positive ions such as Al, Mg, Ca, H, or the like are bonded ascounter ions to the tetrahedral structure of the bond formed betweensilicic acid, which is the base unit, and oxygen. In the case ofshirasu, since it is already calcinated by magma, there is lessprobability that the metallic ions that have been encapsulated in themineral silicate lattice site travel (i.e., exchange); however, thehydrogen ions that have been encapsulated in the lattice are able totravel. The mineral silicate configuring shirasu has a porouspumice-like constitution, and has naturally water-absorbing properties.In addition, aluminum oxide included within mineral silicate has highwater-retentiveness, and hydrogen ions are trapped within the mineralsilicate lattice. Such mineral silicate has a property as an ionexchange body to take in hydrogen ions bonded to water moleculesincluded in the air, and in exchange, emit encapsulated hydrogen ions,H₃O⁺.

[0015] Furthermore, aluminum oxide (AI₂O₃), which bonds to silicic acidto configure mineral silicate, has a porous constitution with highmoisture-retentiveness, water-retentiveness, and gas absorptive power.Accordingly, it is possible to take moisture (water molecules) includedin the air into the mineral silicate lattice and retain it for a longtime, continuously exchanging ions. In particular, the fact that thereis an abrupt increase in the minus ions count when measurement is madefollowing a certain interval after application of a water mistinsinuates that mutual reaction of hydrogen ions in the air with shirasumaterial is facilitated to enhance the negative charge of the air on theinterface, and thereby increase the amount of minus ions.

[0016] The present invention utilizes the minus ion generating effect ofwall material having natural shirasu as a main component. The firstaspect of the present invention provides a wall panel comprising a baselayer, and an application layer, which results from applying(plastering) onto said base layer a wall material having volcanic ejectaas a main component, which is comprised of mineral silicate includingsilicic acid and aluminum oxide; wherein within said application layer,ion exchange between moisture in air and the mineral silicate isperformed generating three to six times as many minus ions as the minusions included in the air under natural conditions.

[0017] As described above, due to the weak ion exchange functionalitywith the mineral silicate included within volcanic ejecta (shirasu) andhigh water-retentiveness by the porous constitution thereof, H₃O+ isconstantly emitted to the interface between the wall panel and the air,negatively charging that air and thereby generating the same amount ofminus ions.

[0018] The application material having volcanic ejecta (shirasu) as amain component is made by mixing 4 to 5 parts by weight of a bindingagent relative to 10 parts by weight of non processed shirasu, adding anappropriate amount of water thereto, and kneading them. As a result,cracks and the like do not occur, and in addition to functioning as anapplication material for walls, the ion exchange functionality andwater-holding capacity of shirasu can be maintained. In addition, it ispossible to secure a wide area and efficiently generate minus ions atthe surface through internal ion exchange functionality by applying soas to make a flat surface.

[0019] A second aspect of the present invention provides a minus iongeneration system comprising a wall surface to which a wall materialwith volcanic ejecta as the main component, which is comprised ofmineral silicate including silicic acid and aluminum oxide, is applied;and a humidity control apparatus, which adjusts an amount of moistureincluded in the atmospheric air; wherein a desired amount of minus ionsare generated from said wall surface by adjusting humidity using saidhumidity control apparatus and thereby controlling the ion exchange ratedue to mineral silicate.

[0020] By combining such a wall comprising shirasu material with thehumidity control apparatus, it is possible to artificially increase andcontrol the level of minus ion production at the wall surface. Thissystem is based on the discovery that the amount of minus ions producedfrom the wall applied with a wall material having shirasu as the maincomponent during the rainy season or when there is high humidity, iseven higher than normal. Such humidity control apparatus may be an airconditioner including a humidifier or humidity control functionality.

[0021] The minus ion effect is known to ease feelings of exhaustion andtension, improve concentration, and suppress oxidization within thebody; accordingly, the minus ion production system utilizing a wallapplied with wall material having shirasu as a main component can bewidely in used rooms such as relaxation rooms, medical examinationrooms, nursing care rooms. In addition, the minus ion producing systemof the present invention is particularly superior at bringing about sucheffects when applied in densely populated living spaces such asapartments and condominiums. It is possible to maintain high minus ionconcentration in a room and create a comfortable living space.

[0022] Moreover, in the case where wall material having shirasu as amain component is used in exterior wall applications, the number ofminus ions in the air of the surrounding residential area is increasedand provides an improved environment for the entire region.

[0023] The secondary effect that shirasu has of producing active oxygenspecies (or oxygen free radicals) depends much on the titanium oxideincluded within the mineral silicate that configures shirasu. Thechemical species existing as active oxygen species and also as freeradicals is referred to as oxygen free radicals. It is well known thatsuch active oxygen species has strong oxidation power and correspondinggermicidal power, and an organic material decomposing power, and throughcatalytic reaction with targeted organic material or chemical species,promotes germicidal properties, decomposition, and a deodorizing effect.

[0024] Titanium oxide is also well known that it performs aphotocatalytic reaction with natural light, illuminated lights, etc.indicating an outstanding effect of preventing from becoming dirty. Byusing a wall material, which has shirasu included within naturaltitanium oxide as a main component, for interior decorations in rooms,the effects of naturally preventing from becoming dirty, cleaning theatmospheric air in rooms, and deodorizing without use of chemical agentsmay be brought out.

[0025] By applying a wall material having shirasu as a main component,which naturally includes such component, to make a flat surface, it maybe used as a natural air filter.

BRIEF DESCRIPTION OF DRAWINGS

[0026] The above-mentioned and other features and results of thisinvention will become more apparent by referencing the followingdetailed description of the invention taken in conjunction with theaccompanying drawings, wherein:

[0027]FIG. 1 is a diagram describing ion exchange functionality of awall surface applied a wall material having shirasu as a main component,according to the present invention; and

[0028]FIG. 2 is a photomicrograph of shirasu molecules.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0029]FIG. 1 is a diagram describing a mechanism producing minus ions atthe wall/air interface through the interactive reaction of the wallsurface that has been applied a wall material having the naturalvolcanic ash material shirasu as a main component and moisture in theair.

[0030] Wall material 13, which is widely spread upon base layer 11,comprises 50 to 65% dried natural volcanic ash material shirasu, 30 to40% binding agent, 3 to 10% clay component, 5 to 10% shirasu balloonsand 1 to 5% fibers for plastering. These materials are kneaded togetherwith an appropriate amount of water securing a sufficient surface areathrough application to base layer 11.

[0031] Dried shirasu is obtained by screening, such as with a wiresieve, natural shirasu that has been collected to give particles havinga diameter of approximately 5 mm or smaller, removing impurities, anddrying. Gypsum plaster, for example, may be used as the binding agent(binder). The clay component is to give plasticity during theapplication process, and in a preferred embodiment, clay includinghydrous mineral silicate in the constitution thereof is employed. Sincesuch viscosity shows plasticity as moisture is taken on, and it hardensas it dries, non processed volcanic ash sediment shirasu is suitablewhen made into a coating material. More specifically, a clay componentincluding silicon dioxide, aluminum oxide, iron oxide, magnesium oxide,calcium oxide, titanium oxide, or the like as a constituent is used.Such a clay component has particularly superior adhesive properties,plastic properties, and dispersion properties, and has a pH 5.9,plasticity index of 22.1, and viscosity of 74 μ 97% Pass.

[0032] Shirasu balloons are also included within the dried shirasu,which allows the finished surface of the wall material to have a softfeel to it. The fiber for plastering functions as a binder and acts toprevent cracks in surfaces; here, hemp fiber or straw (wara) fiber isemployed. If necessary, after application of the wall material, 0.08 to2% plant-derived paste is applied in order to prevent degradation of thesurface due to excessive drying. The plant-derived paste may comprise amixture of (0.03 to 1%) cotton wool and (0.05 to 1%) “tsunomata” (redalgae), which has been boiled with seaweed and formed into a powder.

[0033] In addition to this, an adhesion-reinforcing agent with a basicingredient of natural cellulose (pulp fiber), or an organic pigment maybe added.

[0034] The amount of binding agent should be 4 to 5 parts by weightrelative to 10 parts by weight of the dried shirasu. This allowshardening properties and adhesive properties to be imparted to the driedshirasu. The amount of clay component should be 1 to 1.7 parts by weightrelative to 6 parts by weight of the dried shirasu.

[0035] Although the dried shirasu has been sifted, it comprises largeparticles, medium particles, and small particles. Large particles areclassified as having a diameter of approximately 1.1 mm to 2.3 mm,medium particles as having a diameter of approximately 0.2 mm to 1.0 mm,and small particles as having a diameter of approximately 0.1 mm orsmaller. The dried shirasu included in wall material 13 of FIG. 1comprises approximately 5% large particles, approximately 28% mediumparticles, and approximately 57% small particles.

[0036] The main component of the shirasu is silicic acid and the ratiowith included components is between 65 and 73%. Since silicic aciditself has its own property of taking on negative electric charge it isgiven with a positive ion metal (such as aluminum, iron, magnesium,titanium, manganese) that takes on a positive charge, and is bonded withpositive ion calcium, sodium, potassium, hydrogen, or the like, toconfigure a mineral silicate having neutral crystallization. Shirasu isa naturally calcinated white-colored sand-like sediment resulting fromthis crystallization being exposed to the heat of magma in accordancewith volcanic activity; wherein mineral silicate, which is a componentthereof, has a structure where positive ions such as Al, Mg, Ca, H orthe like are bonded as counter ions to the tetrahedral structure of thebond formed between silicic acid, which is the base unit, and oxygen. Ofthese ions, the positive metallic ions barely travel due to thecalcination by magma, however, the hydrogen ions are able to travel.Accordingly, additional hydrogen ions are taken in to the silicatelattice site comprising a polymer structure, and in exchange, hydrogenions there included are emitted, becoming what is referred to as theobject of ion exchange.

[0037] In addition, alumina (aluminum oxide or Al₂O₃), which isgenerated in the course of the calcination process by magma, occupies 12to 16% of the components of shirasu. Due to the large porous structureof the surface of alumina, water adsorbability and gas adsorbability ishigh. In conformity with such characteristics of alumina, the shirasuhas high water-holding capacity in addition to ion exchangefunctionality.

[0038] In FIG. 1, aeroionization is caused by various contributingfactors in the air. For example, not only the air itself, but moisturewithin the air separates into pairs of plus and minus ions due toionization of the air caused by ultraviolet rays and/ or due to thephoto-electric effect of sun rays with specific wavelengths.Accordingly, even in conditions where wall material having shirasu as amain component is not being used, when humidity is approximately 50%,there exists 300 to 500 minus ions per cc in the air.

[0039] Meanwhile, as shown in FIG. 1, if wall material 13 having shirasuas a main component is being used, H₃O⁺, a plus ion in the air reactswith the mineral silicate structuring wall material 13 at the interfaceof wall material 13. More specifically, when positive ions of H₃O⁺ inthe atmospheric air attempt to be captured in the silicate lattice ofthe shirasu wall surface, the mineral silicate releases hydrogen ionshaving the same sign or a chemical species corresponding thereto. Thishydrogen (H⁺) reacts with the water molecules to again produce H₃O⁺, andthis newly produced H₃O⁺ is again captured in the site of the silicatelattice. Through such a chain reaction progressing throughout theinterface of the shirasu wall, positive ion exchange continues to berepeated within the wall material having shirasu as a main component,while the successively produced positive ions H₃O⁺ bond to the watermolecules existing within the mineral silicate, form clusters of H₃O⁺(H₂O)_(n) ions that take on a positive charge, and become a surfacepotential film on the surface of the wall. This potential allows theamount of minus ions near the wall surface to increase.

[0040] Such ion exchange functionality becomes possible through thehydro-retentive properties and gas adsorptive properties of the porouspumice-like mineral silicate; moreover, use as a wall material isthought to increase interface with the air and further facilitateproduction of minus ions at the interface.

[0041]FIG. 2 is a photomacrograph of shirasu molecules having a diameterof approximately 0.6 mm. As it is clearly shown in this photograph, thestructure has such extreme precision and depth that it is almostunthinkable that this is an artificially produced material. Since it ispossible to use such shirasu particles without processing, together withsufficiently maintaining ion exchange functionality, such porousproperties allow wall material 13 to function as a type of air filter.

[0042] In order to demonstrate the minus ion generating effect of wallmaterial 13 where shirasu has been made a main component according tothe present invention, various measurements have been carried out.

[0043] <Test 1>

[0044] In six model houses (A through F) where wall material 13 havingshirasu as a main component is used for interior decoration, minus ionmeasurement is performed for rooms where shirasu wall material 13 isused and for rooms where it is not used, respectively. These modelhouses are all located within Yokohama. Model houses A, B, and C of thesix model houses are measured under the conditions where temperature is6.5° C. and humidity is 50.5%; model houses A, D, E, and F are measuredunder the conditions where temperature is 26° C. and humidity is 68%.

[0045] The rooms to be measured (both the rooms using shirasu wallmaterial and the rooms that do not) are kept completely closed from theday before. As to measurement positions, measurement is performed foreach room at a fixed position 50 cm above the floor surface at themiddle of the room. In addition to the middle of each room, anadditional measurement is performed in a fixed position approximately 50cm away from the wall in each of model houses A, D, E, and F. An ionmeter IC-1000 made by Universal Ltd. is used as the measuringinstrument. TABLE 1 Measurement under conditions where Temperature =6.5° C. and Humidity = 50.5% MAXMUM/ MIMIMUM IN MIDDLE OF FINISHINGMATERIAL MODEL MEASUREMENT ROOM FOR INTERIOR HOUSES PLACES (IONS/cc)AVERAGE DECORATION A Six-Jyo 1270/780 1025 Shirasu wall (Two-storyJapanese-style room wooden house (approximately 12 m²) Eight-Jyo 340/240290 Red pine board wall Western-style room (approximately 16 m²) BSix-Jyo 1180/790 985 Shirasu wall (Two-story Japanese-style room woodenhouse) (approximately 12 m²) Eight-Jyo 480/280 380 Cedar board pastedwall Western-style room (approximately 16 m²) C Six-Jyo 1870/1340 1605Shirasu wall (3rd floor in Japanese-style room eight-story SRC(approximately 12 m²) house) Eight-Jyo 480/280 550 Cedar board pastedwall Western-style room (approximately 16 m²)

[0046] TABLE 2 Measurement under conditions where Temperature = 26° C.and Humidity = 68% MESUREMENT Center in FINISHING M. H. PLACES roomAverage 50 cm from wall Average MATERIAL A Six-Jyo 1230/750  9902150/1350 1750 Shirasu wall (Two-story Japanese-style room wooden house12 m² Eight-Jyo 800/420 610 860/470 665 Plywood Western-style room wall16 m² D Six-Jyo 1410/990  1200 1900/1430 1665 Shirasu wallJapanese-style room 12 m² Twelve-Jyo 880/470 675 1180/750  965 PBWestern-style room 24 m² E Six-Jyo 1350/990  1170 1680/1140 1410 Shirasuwall Japanese-style room 12 m² Five-Jyo hallway 950/680 815 1010/790 900 Vinyl cloth 10 m² wall F Six-Jyo 3450/2450 2950 3900/2900 3400Shirasu wall Japanese-style room 12 m² Seventeen-Jyo 1010/720  8651150/800  975 PB Western-style room 34 m²

[0047] As shown in Tables 1 and 2, it is clearly shown that there aredifferences between rooms using wall material having shirasu as a maincomponent and rooms where it is not used. As shown in Table 1, in thecase of relatively low humidity (approximately 50%) within rooms notusing wall material having shirasu as a main component, ion measurementcounts range between 300 ions per cc and 500 ions per cc, which matchesthe number of the ions that are found in the normal air of an averagehouse. In contrast, in model houses A to C, rooms using wall materialhaving shirasu as the main component have minus ion levels that are onedigit higher, approximately three or more times normal levels.

[0048] Moreover, even if the humidity is high (e.g., humidity of 68%),effects of the generated minus ions due to the shirasu wall continue.Other than this, there is a tendency for the number of the generatedminus ions to increase as the humidity increases.

[0049] As shown in Table 2, the number of minus ions found in the air ofeach room not using the shirasu wall is somewhat higher, between 600ions per cc and 850 ions per cc with the higher humidity. On the otherhand, there are between 1000 ions and 1200 ions in the middle of theroom in those rooms using the shirasu wall, and these numbers are notvery different from those in the case where humidity is 50.5%; however,it is found that when measured at the position 50 cm away from theshirasu wall, minus ions are generated at a rate of between 1400 per ccand 1800 per cc. It is considered that this phenomenon emanates from thefact that the rate of ion exchange at the interface between the shirasuwall and the atmospheric air increases as temperature rises; thusadditional minus ions are continuously generated at the surface of thewall.

[0050] <Test 2>

[0051] The generated state of the minus ions inside those rooms usingwall material 13 having shirasu as the main component on the wallsurface is observed at a low temperature and at a high temperature,respectively, by deliberately changing the humidity in the entire room.Using an ion meter IC-1000 made by Universal Ltd., measurement isperformed at a height of 50 cm above the floor in the middle of a 12m²room. The measurement results are shown in Table 3. TABLE 3 Humidity 62%72% Number of Minus ions 1135/cc 1205/cc (Average)

[0052] In general, it is said that the number of the minus ionsdecreases during rainy days. Since minus ions within living spaces existgenerally adhered to clusters of minute water molecules, the number ofminus ions increases as the number of clusters increases. However, onrainy days, there is a rejoining of the water molecules which causes thenumber of clusters to decrease; accordingly, the number of the minusions decreases.

[0053] On the other hand, in rooms that use wall material 12 havingshirasu as the main component, even on rainy days, a stable number ofgenerated minus ions is indicated. Other than this, there is a tendencyfor the count of the generated minus ions to increase as humidityincreases. The results shown in Table 3 are measurements obtained in themiddle of the room; however, considering the results shown in Table 2,it is estimated that the number of generated minus ions furtherincreases in vicinity of the shirasu wall as the temperature increases.

[0054] The mineral silicate configuring the shirasu is a porouspumice-like material having favorable moisture absorption properties andwater holding properties, and performs ion exchange at a fixed rate.More specifically, there is cyclical chain reaction of hydrogen ionsadhered to water molecules along with moisture included in the air beingtaken into the silicate lattice site, ion exchange being performed withhydrogen ions included therein, additional positive ions being generatedat the interface, and the surrounding air being negatively charged. Evenif the number of the clusters included in the air decreases due to rain,the ion exchange chain at the shirasu wall surface is maintained,consequently showing a high rate of minus ion generation.

[0055] By utilizing such properties of the mineral silicate configuringthe shirasu and combining a wall surface applied with wall materialhaving shirasu as the main component with a humidity control apparatusfor controlling humidity, it is possible to construct a minus iongenerating system, which provides a desired minus ion environment. Inthe case where this system is used in an average house, the humidity ofa room is adjusted to a certain appropriate value, for example, on drydays, and the inside minus ion generation rate is controlled, making itpossible to provide a refreshing space.

[0056] In addition, by using this system in a medical examination roomor counseling room, it becomes possible to make a patientpsychologically stable, promote physical living active potential, andpromote cellular regeneration.

[0057] <Test 3>

[0058] The generated state of minus ions when a water mist is sprayedwith an atomizer, etc. onto a wall surface applied with wall materialhaving shirasu as the main component is observed. The area of the roomfloor is 12 m², and the surface area of the shirasu wall is 29 m². Awater mist is applied across the entire surface of the shirasu wall at arate of 69 ml/m². Measurements are made both before and ten minutesafter the water mist is applied. TABLE 4 10 minutes after Before sprayspray Position 50 cm above 1500/1020 2600/1850 floor in middle of room1260 ions/cc in 2225 ios/cc in average average Position 50 cm above1650/1350 3200/1910 and 50 cm apart from 1500 ions/cc in 2555 ions/cc inwall surface average average

[0059] It is also found here that due to the existence of the shirasuwall, even before the mist is applied, at least three times the amountof minus ions generally included in the atmospheric air (i.e., between300 and 500 ions per cc) are generated. An average of 9250 minus ionsper cc are recorded at a position 50 cm away from the shirasu wall whena water mist is applied to such a shirasu wall; however, this abruptincrease is temporary, and does not emanate due to the ion exchangefunctionality of the shirasu wall. Rather, the measurement resultsobtained when measurement is made following a certain interval afterapplication of the water mist supports the minus ion generation resultsof the shirasu wall. 10 minutes after the mist is applied, when thenumber of the minus ions is measured in the middle of the room and at aposition 50 cm away from the shirasu wall, whether in the middle of theroom or 50 cm away from the wall, a minus ion level that is 1.7 timesthat before the mist is applied is recorded.

[0060] The results of the generated minus ions when a water mist isapplied to the surface of the wall having shirasu as the main componentshould be distinguished from the Lennard effect. In order to show thatthe increase in minus ions from the shirasu wall does not emanate fromthe Lennard effect, a comparative example is given, where a water mistis applied at the same rate to a glass window and a plywood wall,respectively, within a room not using wall material having shirasu asthe main component; the minus ion levels are then measured three minutesafter the water mist is applied and ten minutes after the water mist isapplied. The measurement results are shown below. TABLE 5 3 minutesafter 5 minutes after Before spray spray spray Glass surface 730/530500/350 620/480 (630 in average) (425 in average) (560 in average)Plywood wall 230/140 530/230 490/130 surface (185 in average) (380 inaverage) (310 in average)

[0061] The increase in the value of minus ions on the surface of theplywood just after the water mist is applied (three minutes later)emanates from the Lennard effect. However, unlike the shirasu wall, theLennard effect due to mist application does not continue for a longperiod of time; accordingly, the number of minus ions decreases tenminutes after the water mist is applied. On the other hand, on thesurface of the glass, the number of the minus ions decreases just aftera water mist is applied (three minutes later), which is can beconsidered as emanating from the fact that water droplets adhere to thesurface of the glass thereby decreasing the number of clusters.

[0062] The results shown in Tables 4 and 5 affirm the superior minus iongenerating effect of the shirasu wall. As described above, the mineralsilicate configuring shirasu is a porous, pumice-like material and hassuperior water-absorbing properties. In the case where water is appliedas a mist with an atomizer or the like, the water and the hydrogen ionsadhered thereto are captured and hydrogen ions that had beenencapsulated are emitted, allowing the discharged hydrogen ions to bondto the water molecules configuring positive potential on the interfaceand again try to enter the silicate lattice site. It is considered thatthe water mist thus applied facilitates such a chain-like ion exchangeprocess, allowing continuous improvement of generation rate of minusions.

[0063] It is well known that minus ions positively influence the healthof the human body. According to the results of measuring, for example,fatigue levels using a flicker meter, it is verified that fatigue levelis low within a room having a level of minus ions on par with those inan average forest, thereby enhancing concentration power. In addition,according to measurement results recording electrical activity on thesurface of the brain using an electroencephalogram, it is indicated thatthere is higher magnitude of alpha-2 waves (between 10 Hz and 12.75 Hz)within a room having more minus ions than an average room, which mayease feelings of tension and allow relaxation.

[0064] In the case where wall material 13 with the shirasu shown in FIG.1 as the main component is used as the interior decoration of a buildingand is applied to a wall surface or a ceiling, since sufficient surfacearea is provided, the ion exchange functionality of the shirasu isbrought out increasing the concentration of minus ions within rooms. Asa result, the following actions are expected: blood purification actionwhereby neutralization of blood having a low pH transformed to bloodhaving a higher pH, which promotes healthy resistance; ataractic actionwhereby intracerebral beta endorphins are activated; modulating actionof the autonomic nervous system for insomnia, headache, climactericdisorder, stiff neck, backache, chronic fatigue, etc.; immune systemenhancement action whereby intestine and liver functions are improved;lung function enhancement action that improves lung function tofacilitate discharge of carbon dioxide and improve oxygen exchange rate;and analgesic action for chronic rheumatism, etc.

[0065] Alleviation of the symptoms of insomnia, hay fever, etc. wasactually reported by people living in the model houses, and it is alsoexpected that the symptoms of asthma and atopic dermatitis due to housedust, cigarette, etc. can be eased. Wall materials having shirasu as themain component can be used in medical rooms, counseling rooms,relaxation rooms, etc. other than average houses because of theataractic action and health maintenance effects thereof.

[0066] It is suitable for the shirasu wall, which absorbs humidity andgenerates minus ions, to be used in houses, in particular, in countrieshaving relatively high humidity and rural areas. Moreover, by using theshirasu wall on a ceiling, not only is humidity absorbed to create acomfortable living space, but also generated minus ions in the air areabsorbed into a human body, and active oxygen within human body aredeoxidized via the mucus membranes and/or capillaries, to help preventoxidation.

[0067] In order to configure a minus ion generation system as mentionedabove, water is directly added to mineral silicate including at leastsilicic acid and aluminum oxide, a predetermined amount of a bondingagent (e.g. gypsum, plaster, etc.), a clay component, shirasu balloons,etc., are kneaded together and applied to wide planes such as thesurface of a wall, a panel, etc. Such application may be performed witha trowel or the like; or it may be performed by spraying with a spraygun, etc. Alternatively, it is also allowable for a brush may be used;no specialized application means is required.

[0068] After the surface of the wall is dried, humidity within a roomwith this wall is controlled. Humidity control is performed using ahumidistat, an air conditioner, an atomizer, etc. In this manner, thenumber of minus ions to be generated from the surface of the wall may beregulated to a predetermined amount.

[0069] In the case where the wall with the shirasu as the main componentis used within a closed room, the effect of generated minus ions isenhanced; however, it may also be used for an exterior wall. In thiscase, since it is positioned within a open space, it may not providegreat increases in the effects of minus ions to those inside room;however, when a wall having shirasu as the main component is used forthe exterior wall of a newly-built building within a newly developedresidential area, an environment with a higher number of minus ions thanthat of an ordinary residential area may be provided for the entiretown.

[0070] An additional effect of wall material 13 having shirasu as themain component is a deodorizing effect and a cleansing effect due togeneration of an active oxygen species (oxygen free radicals). Titaniumincluded as titanium oxide within the shirasu reacts with the hydrogenand humidity (moisture) included in the atmospheric air generates anactive oxygen species. Such an active oxygen species breaks down organicmaterial existing throughout the atmospheric air and moisture and breaksdown odor at their respective source.

[0071] In addition, hydrogen included in the shirasu bonds with oxygengenerating hydroxyl group (hydroxy radicals (.OH)). In addition, contactwith water molecules and oxygen occurring in the course of the exchangeprocess at an electric level that causes a high activation level tooccur and generates an active oxygen species (oxygen free radicals) suchas super oxide anion radicals (.O²⁻). Since the active oxygen species(oxygen free radicals) have strong germicidal properties and organicmaterial break-down properties, a shirasu wall including this reactivesystem provides an enhanced sterilizing, deodorizing, and air-fresheningeffect that freshens air passing through the surface layer and theinside thereof, and therefore functions as a natural air filter to cleanthe air in a room.

[0072] When light is applied to the titanium oxide included in theshirasu and the moisture both inside and outside of the shirasu wallmaterial, what is referred to as a photocatalytic reaction of thetitanium oxide occurs. For example, when an ultraviolet light irradiatesthe titanium oxide, pairs of electron and electron holes are formed, andthe pairs react to oxygen and moisture included in the atmospheric airto generate super oxide ions and/or hydrogen radicals with strongoxidative powers. This is well known as the Honda-Fujishima effect.

[0073] Wall material 13 having shirasu as the main component shown inFIG. 1 essentially includes a titanium oxide, and the mineral silicate,which is porous and pumice-shaped, (especially, an aluminum oxide)includes water. In other words, wall material 13 itself generates anactive oxygen (oxygen free radicals) that functions as an air cleanfilter. Such a filtering function may be further efficiently brought outwhen a titanium oxide is used for the clay component, which is to bemixed in to provide plastic properties.

[0074] Photocatalytic reaction of the titanium oxide may also include afunction bringing out a hyper hydrophilic phenomenon. The ordinarysurface of a titanium oxide has stable hydrophobic property due tooxygen cross linking between titanium atoms; however, when anultraviolet light irradiates the surface of the titanium oxide, part ofcross linking oxygen is eliminated and generates oxygen defects.Dissociative absorption of moisture included in the air is made thereinto produce chemically absorptive water (hydroxyl group) and therebybecomes hydrophilic. Water molecules are then become attached asphysically absorptive water to the hydroxyl group and the hydrophilicproperties are stably maintained. Such hyper-hydrophilization bringsabout prevention of water droplet formation, prevention of tarnishing ofthe wall surface, and the function of self-cleaning with water.

[0075] When the shirasu is used as a wall material and applied to a wideplane, the ion exchange functionality and purifying action of themineral included in the shirasu are efficiently performed, providingexcellent medical and of environmental engineering effects.

1. A wall panel, comprising: a base layer; and an application layer,which is applied to said base layer and which is comprised of a wallmaterial with a volcanic ejecta as the main component, which iscomprised of mineral silicate including al least silicic acid andaluminum oxide; wherein minus ions are generated at the interfacethrough ion exchange between positive ions included within said mineralsilicate and moisture in air.
 2. The wall panel according to claim 1,wherein the amount of generating of minus ions is, per unit volume,three to six times as many as that of minus ions existing in ordinaryair.
 3. The wall panel according to claim 1, wherein said applicationlayer is obtained by mixing 10 parts by weight volcanic ejecta and 4 to5 parts by weight binding agent, adding an appropriate amount of water,and kneading them.
 4. A wall panel, comprising: a base layer; and anapplication layer, which is applied to said base layer and which iscomprised of a wall material with a volcanic ejecta as the maincomponent, which is comprised of mineral silicate including at leastsilicic acid, aluminum oxide, and titanium oxide; wherein an activeoxygen species or oxygen free radicals are generated throughoxidation-reduction reaction of moisture or oxygen included within saidmineral silicate with the help of said titanium oxide that acts as acatalyst.
 5. A wall panel, comprising: a base layer; and an applicationlayer, which is applied to said base layer and which is comprised of awall material with a volcanic ejecta as the main component, which iscomprised of mineral silicate including at least silicic acid, aluminumoxide and titanium oxide; wherein an active oxygen species or oxygenfree radicals are generated through a reaction of moisture or oxygenincluded an air thereto with the help of said titanium oxide that actsas a catalyst.
 6. A minus ion generation system, comprising: a wallsurface to which a wall material with volcanic ejecta as the maincomponent, which is comprised of mineral silicate including at leastsilicic acid and aluminum oxide, is applied; and a humidity controlapparatus, which adjusts an amount of moisture in air; wherein, adesired amount of minus ions are generated from said wall surface byadjusting humidity using said humidity control apparatus and therebycontrolling the ion exchange rate on said wall surface.
 7. The minus iongeneration system according to claim 6, wherein said humidity controlapparatus is a humidifier.
 8. The minus ion generation system accordingto claim 6, wherein said humidity control apparatus is an airconditioner with a humidity control function.
 9. The minus iongeneration system according to claim 6, wherein said system is used in aresidential space.
 10. A minus ion generation method, comprising thesteps of: forming a wall surface by adding a predetermined amount ofbinding agent and an appropriate amount of water to a volcanic ashsediment, which comprises mineral silicate including at least silicicacid and aluminum oxide, kneading them, and applying to an arbitraryplane; and generating minus ions on said application surface through anatural reaction with moisture in air at room temperature causing ionexchange.
 11. The minus ion generation method according to claim 10,further comprising a step of regulating the size of each particle ofsaid volcanic ash sediment to be 5 mm or less in diameter, and dryingsaid volcanic ash by performing calcination thereupon at temperaturesbetween 100° C. and 800° C.
 12. The minus ion generation methodaccording to claim 10, further comprising a step of increasing theamount of the minus ions generated by applying a water mist to said wallsurface to promote ion exchange.
 13. The minus ion generation methodaccording to claim 10, further comprising a step of generating a desiredamount of minus ions at said application surface by adjusting humidityin a building so as to control the amount of said ion exchange; whereinsaid wall surface is an inner wall surface of said building.
 14. Theminus ion generation method according to claim 10, wherein saidapplication surface is an outer wall surface of a building.
 15. A methodof using a wall surface as an air clean filter, comprising the steps of:forming a wall surface by adding a predetermined amount of binding agentand water to a volcanic ash sediment, which comprises mineral silicateincluding at least silicic acid, aluminum oxide and titanium oxide,kneading them, and applying to an arbitrary plane; and generating anactive oxygen species or oxygen free radicals throughoxidation-reduction reaction of moisuture or oxygen with the help ofsaid titanium oxide that acts as a catalyst.